Hydrophobic silica

ABSTRACT

Hydrophobic, pyrogenically produced silica having a tamped density of 55 to 200 g/l is produced by hydrophobizing pyrogenically produced silica and then compacting it. The silica may be used for the production of dispersions.

REFERENCE TO A RELATED APPLICATION

[0001] This application claims the benefit of provisional applicationNo. 60/171,667 filed Dec. 27, 1999 which is relied on and incorporatedby reference.

INTRODUCTION AND BACKGROUND

[0002] This invention relates to a hydrophobic, pyrogenically producedsilica, to a process for the production thereof and to the use thereof.

[0003] It is known to compact hydrophilic, pyrogenically produced silica(EP 0 280 854 B1). Disadvantageously, as tamped or bulk densityincreases, thickening action declines in a linear manner. Dispersibilityalso falls as density increases. This results in unwanted speckling.Thus, once compacted, a hydrophilic, pyrogenically produced silica mayonly be used for a limited number of applications.

[0004] It is therefore an object of the present invention to avoid theproblems of compacted, hydrophobic, pyrogenically produced silica of thepast.

SUMMARY OF THE INVENTION

[0005] The above and other objects of the present invention can beachieved by developing a hydrophobic, pyrogenically produced silicahaving a tamped density of 55 to 200 g/l.

[0006] The tamped density is preferably from 60 to 200 g/l.

[0007] A feature of the present invention is a process for theproduction of the hydrophobic, pyrogenically produced silica having abulk density of 55 to 200 g/l, which process is characterised in thatpyrogenically produced silica is hydrophobized using known methods andthen compacted.

[0008] Hydrophobing can preferably be performed by means of halogen-freesilanes. The chloride content of the silica can be less than or equal to100 ppm, preferably from 10 to 100 ppm.

[0009] Compaction can be performed by means of a roller compactor.Compaction can preferably be performed by means of a belt filter pressaccording to EP 0 280 851 B1, which reference is relied on andincorporated by reference.

[0010] The hydrophobic, pyrogenically produced silica used for purposesof the present invention can be, for example, the silicas known as:

[0011] Aerosil R 812 or Aerosil R 812S, having the group —O—Si(CH₃)₃

[0012] Aerosil R 202, Aerosil MS 202, Aerosil MS 202, Aerosil R 106 orAerosil R 104 having the group

[0013] Aerosil R 805 having the group

[0014] These are commercially available products from Degussa Hüls AG.

[0015] The hydrophobic, pyrogenic silica according to the inventionhaving a tamped density of 55 to 200 g/l exhibits the followingadvantages:

[0016] Transport costs are distinctly lower as a result of the highertamped density.

[0017] Once dispersed, the silica according to the invention is in theform of relatively small aggregates. In other words, the dispersions aremore finely divided because the silica according to the invention ismore readily dispersible.

[0018] The dispersions produced using the silica according to theinvention exhibit a lower Grindometer value.

[0019] Both UV transmission transparency and visual transparency of thedispersions are distinctly improved by using the silica according to theinvention.

[0020] Dispersions containing the silicas according to the inventionexhibit distinctly increased stability because the tendency towardssettling is distinctly lower.

[0021] Another advantage of the silica according to the invention isreduced dusting during incorporation and the distinctly reducedincorporation or wetting time in, for example, liquid systems.

[0022] In comparison with hydrophobic, pyrogenic silica of a lower bulkdensity, the hydrophobicity of the silica according to the invention isunchanged. Thickening action is also unchanged.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be further understood with referenceto the following detailed embodiments thereof.

EXAMPLE 1

[0024] Various hydrophobic, pyrogenically produced silicas areinvestigated, wherein different compaction states are compared.

[0025] The following definitions apply: bulk = pulverulent, unmodifiedsilica CF = silica compacted with a Carter filter VV 60 = silicacompacted to a tamped density of approx. 60 g/l VV 90 = silica compactedto a tamped density of approx. 90 g/l

[0026] Aerosil grades R 202, US 202, US 204, R 812, R 812S and R 805 areinvestigated. The results are shown in Table 1.

[0027] As evaluated by the Corning Glass methanol wettability method,the degree of compaction has virtually no appreciable influence onhydrophobicity. Viscosity also exhibits no clear systematic dependencyupon tamped density. Especially for R 812, dispersibility improves withincreasing density. R 812S, which contains more SiOH groups than R 812,exhibits the above phenomenon less markedly.

[0028] US 202 and US 204 have very comparable theological properties andare inferior to AEROSIL R 202.

[0029] Surprisingly, the compacted variants, in particular of R 812, R202 and US 202/4, exhibit an incorporation time reduced by up to half.The compacted silicas moreover exhibit reduced dusting. 444701 444702444703 444704 444705 444706 444707 444708 AER AER AER AER AER AER AERAER 444709 444710 444711 202 202 202 202 805 805 805 805 AER812 AER812AER812 PA Test method CF CF VV60 VV90 bulk CF VV60 VV90 bulk CF VV600330 Viscosity, epoxy before cure 459 456 382 430 190 181 185 178 0335Viscosity, epoxy after cure 54.4 54.7 49.4 52.8 42 41.7 39 43 0340Thickening action 11.7 13.3 11.5 0410 Grind motor value 127 102 92 0420Methanol wetability 0701 Tamped density 45 50 51 75 44 62 55 68 45 44 500920 Agglemerate strength 11 20 18 15 15 20 0930 Hand: |sic|sieveoversize 0 24 4 27 0 36 7 19 0 0 0955 Effectiveness 258 274 203 266 235260 236 258 166 185 169 0965 Effectiveness(UT) 280 290 226 295 281 270288 197 213 209 0975 Settling(effectiveness) 15 15 15 8 10 15 10 5 13 158 444712 444713 444714 444715 444716 AER AER AER AER AER 444717 444718444719 444720 444721 444722 444723 812 812S 812S 812S 812S US202 US202US202 US204 US204 US204 US204 PA Test method VV90 bulk CF VV60 VV90 bulkCF VV60 bulk CF VV60 VV90 0330 Viscosity, epoxy 350.4 377.6 380.8 379.2350.4 358.4 368 before cure 0335 Viscosity, epoxy after cure 50.7 45.945.3 49.9 47 52.6 50.7 0340 Thickening action 11.1 17.3 17.3 18.2 170410 Grind motor value 77 93 110 110 100 0420 Methanol wetability 0701Tamped density 73 49 50 58 75 39 50 67 44 45 57 71 0920 Agglemeratestrength 22 28 10 15 16 23 0930 Hand: |sic|sieve oversize 12 0 0 0 4 027 36 0 0 3 20 0955 Effectiveness 159 168 169 187 209 320 304 320 186193 192 201 0965 Effectiveness(UT) 225 201 200 216 235 336 327 346 223225 225 230 0975 Settling(effectiveness) 5 8 8 3 0 15 10 3 10 10 10 10

EXAMPLE 2

[0030] Investigation of the Influence of Higher Compaction onApplicational Properties AE R 812, AE R 812, AE R 812, compactedcompacted uncom- RHE RHE pacted UB 3847-2 UB 3847-3 UB 3847-1 (4) (5) AER 812 10 kg 15 kg 20 kg RHE sack sack sack specific. Tamped density (DINISO g/l 50 87 106 approx. 787/11) 50 Effectiveness, ethanol 184 214 209216 1) (0955) Effectiveness (UT), 218 260 290 236 1) ethanol (0965)Settling vol. % 10 1 1 1) (effectiveness, high- speed mixer)

[0031] 1. Determined on standard sample (UB 3391)

[0032] RHE in the above table indicates the Rheinfelden plant located inGermany.

[0033] Rheological Testing:

[0034] Polymer: Araldit M (biphenol-1-expoxy resin by Ciba-Geogy, in theform of clear yellow liquid).

[0035] Thixotroping agent: R 202 and R 812 Additive:—

[0036] Sample A R 812 10 kg 2-10123 Sample production date: 24.02.1994Spindle: 5 Storage time 5 rpm 50 rpm in days [mPa*s] (mPa*s) T.I. SampleA R 812 10 kg 2-10123 0 16600 4460 3.72 80-85 μ Sample A R 812 15 kg1.0/8 min 0 15100 4060 3.72 50-60 Sample AR 812 20 kg 0.6/14 min 0 151004020 3.73 50-60 μ

[0037] Compaction may amount to a type of predispersion. Accordingly,effectiveness values rise with tamped density, i.e. the particleseffectively present in the ethanol dispersion become smaller and thecompacted samples exhibit distinctly less settling. Any suitable organicsolvent can be used to form the dispersion.

[0038] The compacted samples accordingly have a more favourableGrindometer value in Araldit. However, since the larger particles have adecisive influence on thickening action, the property declines slightlyon compaction.

[0039] It may be seen from the graph of effectiveness values that, whilethe highly compacted AEROSIL R 812 sample may indeed still be broken upwith the Ultra-Turrax mixer (0965), it can no longer be broken up withthe high speed mixer (0955). Due to the smaller surface area of AEROSILR 202 (and to the consequently theoretically improved dispersibility),this phenomenon hardly occurs with AEROSIL R 202.

[0040] As compaction rises, the particles effectively present in anethanol dispersion thus become smaller and 90° angle scattering risesdue to Rayleigh scattering. Total scattering (over all angles), however,falls and the samples become distinctly more transparent on visualinspection, as is also substantiated by the UV transmission spectra.

[0041] Compaction has no influence on hydrophobicity, which in each casesubstantially corresponds to that of the standard sample.

EXAMPLE 3

[0042] Investigation of the Influence of Higher Compaction onApplicational Properties. AE R 202, AE R 202, AE R 812, compactedcompacted uncompacted RHE RHE UB 3848-1 UB 3848-2 UB 3848-3 2-020242-01024- 2-01024- AE R 202 10 kg (2) (3) RHE sack 15 kg sack 20 kg sackspecific. Tamped density (DIN ISO 787/11) g/l 51 93 119 approx. 60 3)Effectiveness, ethanol (0955) 319 334 336 334 1) Effectiveness (UT),ethanol (0965) 346 365 373 339 1) Settling vol. % 10 5 1 (effectiveness,high-speed mixer)

[0043] The compacted AEROSIL R 202 samples behave in a similar manner tothe compacted AEROSIL R 812 samples.

[0044] Reference is thus made to Example 2 with regard to thediscussion.

[0045] The parameter of “effectiveness” reported in the tables hereinrelates to the high degree of fineness of the particle. This istherefore an indicator of high transparency and good stability of theresulting dispersions.

[0046] Further variations and modifications of the foregoing will beapparent to those skilled in the art and are intended to be encompassedby the claims appended hereto.

[0047] German priority application filed December 22, 2000 199 61 933.6is relied on and incorporated herein by reference.

1. A hydrophobic, pyrogenically produced silica, having a tamped densityof 55 to 200 g/l.
 2. The hydrophobic, pyrogenically produced silicaaccording to claim 1 having a tamped density of 60 to 200 g/l.
 3. Thehydrophobic, pyrogenically produced silica according to claim 1 which ishydrophobicized by reaction with a halogen-free silane.
 4. Thehydrophobic, pyrogenically produced silica according to claim 4 whereinsaid silica has a chloride content of less than or equal to 100 ppm. 5.A process for the production of the hydrophobic, pyrogenically producedsilica as claimed in claim 1, comprising hydrophobizing pyrogenicallyproduced silica and then compacting said silica.
 6. The processaccording to claim 5 wherein said compacting is by roller compactor. 7.The process according to claim 5 wherein said compacting is by beltfilter press.
 8. A hydrophobic, pyrogenically produced silica havingbeen produced by the process of claim
 5. 9. Use of the hydrophobic,pyrogenically produced silica as claimed in claim 1 for the productionof dispersions.
 10. A dispersion of a hydrophobic, pyrogenicallyproduced silica produced by the process of claim 5.